The Apple Snail as a Biological Control Agent for Weed Management in Ebro Delta Rice Paddies

In the Ebro Delta, Echinochloa spp., Cyperus difformis, and Heteranthera reniformis severely impair rice establishment, while the invasive apple snail (Pomacea spp.) exerts selective herbivory. This study evaluated whether alternative apple snail management strategies could contribute to weed suppression as part of an integrated weed-snail management strategy. Field experiments were conducted on three rice farms during the 2024–2025 cropping season using a 5 × 5 Latin square design. Five treatments were compared: a standard strategy with full snail and weed control (FSC + H), a full snail control omitting herbicides (FSC), a strategy with snail control restricted to post-harvest either without herbicides (OST) or with herbicides (OST + H), and free snail herbivory followed by a targeted molluscicide application prior to rice seeding in June (JST). Weed density, rice establishment and phenological development (BBCH scale) were assessed. Fourteen days after the herbicide treatment, FSC + H, OST + H, and JST achieved complete weed suppression, whereas OST exhibited 573.53 and 53.80 weed plants·m−2 , respectively. Uncontrolled weed pressure in herbicide-free FSC control led to crop failure (4.6 rice plants·m−2). Conversely, the herbicide-free JST strategy, which utilized high snail densities during false seeding and applied saponin just before sowing, secured a high crop density of 99.93 plants·m−2. This represented a non-significant proportional reduction in rice establishment of only 3.85% compared to the FSC + H standard (103.93 plants·m−2). These findings indicate that Pomacea spp. may contribute to integrated weed management in Mediterranean flooded rice systems in already infested fields.